Understanding IMAP/SMTP password's storage in keychain

iCloud is not used/enabled, nor iCloud Keychain does this here.

My tries to get some understanding of IMAP/SMTP password storage in keychain. For those IMAP/SMTP accounts taken over from previous OS X version installed Sierra seems to have in Local Items keychain a pair: com.apple.account.IMAP.accountsync and com.apple.account.IMAP.password (plus such pair for SMTP). For IMAP/SMTP account created today (Sierra 10.12) one can find in Local Items just ...IMAP.password and ....SMTP.password. Where this difference from? Is .accountsync-type obsolete now?

I can also see that for every Goole mail account only .accountsync entry is present in keychain. But Google accounts have special handling in mac OS not at this point. So maybe presence of only .accountsync for Google mail accounts is in-line of this design.